Communicable Disease and Infectious Disease.
Chapter 25 Communicable Disease Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of
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Elsevier Inc. Principles of Infection and Infectious Disease Occurrence Biological and epidemiological principles ➢ Multicausation ➢ Spectrum of Infection ➢ Stages of Infection ➢ Spectrum of disease occurrence Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 2 Multicausation Disease etiology is complex and multicausal. An infectious agent alone is not sufficient to cause disease; the agent must be transmitted within a conducive environment to a susceptible host. Host Environment Agent Epidemiological Triad Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 3 Spectrum of Infection Not all contact with an infectious agent leads to infection, and not all infection leads to an infectious disease. ➢ ➢ ➢ ➢ Subclinical infection: no overt symptomatic disease (unapparent or asymptomatic) Infections: entry and multiplication of infectious agent in host Infectious disease and communicable disease: pathophysiological responses of the host to the infectious agent, manifesting as an illness (considered a case) Carriers: people who continue to shed infectious agent without any symptoms of disease Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 4 Stages of Infection Latent period ➢ ➢ Communicable period ➢ ➢ Infectious agent has invaded a host and found conditions hospitable to replicate Replication before shedding Follows latency Begins with shedding of agent Incubation period ➢ ➢ Time from invasion to time when disease symptoms first appear May overlap with communicable period Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 5 Stages of Infection (Cont.) Figure 25-1 From Grimes DE: Infectious diseases, St Louis, 1991, Mosby. Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 6 Spectrum of Disease Occurrence Incidence—new cases in a population Endemic—diseases that occur at a consistent, expected level in a geographic area Outbreak—an unexpected occurrence of an infectious disease in a limited geographic area during a limited period of time Epidemic—an unexpected increase of an infectious disease in a geographic area over an extended period of time Pandemic—steady occurrence of a disease over a large geographic area or worldwide Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 7 Chain of Transmission Infectious agents Reservoirs Portals of exit and entry Modes of transmission ➢ Direct ➢ Indirect • Fomites or vectors ➢ Fecal-oral, airborne Host susceptibility Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 8 Chain of Transmission (Cont.) Figure 25-2 Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 9 Chain of Transmission: Part 1 Links of the Chain Definition Factors Infectious agent An organism (virus, rickettsia, bacteria, fungus, protozoan, helminth, or prion) capable of producing infection or infectious disease Properties of the agent: morphology, chemical composition, growth requirements, and viability. Interaction with the host: mode of action, infectivity, pathogenicity, virulence, toxigenicity, antigenicity, and ability to adapt to the host Reservoirs The environment in which a pathogen lives and multiplies Humans, animals, arthropods, plants, soil, or any other organic substance Portal of exit Means by which an infectious agent is transported from the host Respiratory secretions, vaginal secretions, semen, saliva, lesion exudates, blood, and feces Table 25-1 Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 10 Chain of Transmission: Part 2 Links of the Chain Definition Factors Mode of transmission Method whereby the infectious agent is transmitted from one host (or reservoir) to another host Direct: person to person Indirect: implies a vehicle of transmission (biological or mechanical vector, common vehicles or fomite) Airborne droplets Portal of entry Means by which an infectious agent enters a new host Respiratory passages, mucous membranes, skin, percutaneous injection, ingestion, and through the placenta Host susceptibility The presence or lack of sufficient resistance to an infectious agent to avoid or prevent contracting an infection or acquiring an infectious disease Biological and personal characteristics (e.g., gender, age, genetics), general health status, personal behaviors, anatomical and physiological lines of defense, immunity Table 25-1 Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 11 Breaking the Chain of Transmission Controlling the agent Eradicating the nonhuman reservoir Controlling the human reservoir ➢ Controlling the portals of exit and entry ➢ ➢ Quarantine—during incubation period Isolation of sick persons Universal precautions Improving host resistance and immunity Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 12 Types of Immunity Natural immunity: an innate resistance to a specific antigen or toxin Acquired immunity: derived from actual exposure to specific infectious agent, toxin, or appropriate vaccine ➢ ➢ Active acquired: body produces its own antibodies Passive acquired: temporary resistance that has been donated to the host Primary vaccine failure: failure of vaccine to stimulate any immune response Secondary vaccine failure: waning of immunity following an initial immune response Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 13 Types of Acquired Immunity Type Natural How Acquired Length of Resistance Active Natural contact and infection with the antigen May be temporary or permanent Passive Natural contact with antibody transplacentally or through colostrum and breast milk Temporary Active Inoculation of antigen May be temporary or permanent Passive Inoculation of antibody or antitoxin Temporary Artificial Table 25-2 Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 14 Types of Immunity Herd immunity: a state in which those not immune to an infectious agent will be protected if a certain proportion (generally considered to be 80%) of the population has been vaccinated or is otherwise immune Figure 25-3 Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 15 Public Health Control of Infectious Diseases Control ➢ The reduction of incidence (new cases) or prevalence (existing cases) of a given disease to a locally acceptable level as a result of deliberate efforts Elimination ➢ Controlling a disease within a specified geographic area and reducing the prevalence and incidence to near zero ➢ The result of deliberate efforts, but continued intervention measures are required Eradication ➢ Reducing the worldwide incidence of a disease to zero as a function of deliberate efforts (e.g., smallpox in 1977) ➢ No need for further control measures ➢ Only possible under certain conditions Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 16 Criteria for Disease Eradication Human host only; no host in nature Easy diagnosis; obvious clinical manifestations Limited duration and intensity of infection Natural lifelong immunity after infection Highly seasonal transmission Availability of vaccine, curative treatment, or both Substantial global morbidity and mortality rates Cost effectiveness of campaign and eradication Integration of eradication with additional public health variables Eradication imperative over control measures – CDC (1993) Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 17 Notifiable Infectious Diseases in the United States HCP MUST report to local or regional health departments → state health dept. →CDC Reported weekly in the MMWR Go to CDC website for latest listing of diseases: http://www.cdc.gov Note: State health departments have the responsibility for monitoring and controlling communicable diseases within their respective states; they determine which diseases will be reported within their jurisdiction. Those lists might be longer than the CDC’s list. Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 18 Vaccines and Infectious Disease Prevention Immunization is a broad term used to describe a process by which active or passive immunity to an infectious disease is induced or amplified. ➢ Immunizing agents can include vaccines as well as immune globulins or antitoxins. Vaccination is a narrower term referring to the administration of a vaccine or toxoid to confer active immunity by stimulating the body to produce its own antibodies. Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 19 Recommended Immunization Schedules Recommendations for international immunization practices determined by WHO In the United States, AAP and ACIP Current U.S. recommendations found on CDC website: http://www.cdc.gov/vaccines Schedules, footnotes, and educational fact sheets provide guidelines for practice Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 20 Vaccines: Words of Caution Information and recommendations on immunizations and vaccine usage change regularly Vaccine Information Statements (VISs) that explain the benefits and risks must be given out before vaccine is administered— a federal law!! (http://www.cdc.gov/vaccines/hcp/vis/index.html) Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 21 Available Vaccines by Type Live attenuated vaccines (See Textbook Table 25-3) Viral: measles, mumps, rubella, oral polio, vaccinia, yellow fever, varicella Bacterial: BCG (Bacille Calmette-Guérin) Recombinant: oral typhoid Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 22 Available Vaccines by Type (Cont.) Inactivated vaccines (See Textbook Table 25-3) Viral: influenza, polio, rabies, and hepatitis A Bacterial: typhoid, cholera, and plague Subunit (fractional): influenza, acellular pertussis, typhoid Vi and Lyme disease Toxoid: diphtheria and tetanus Recombinant: hepatitis B Conjugate polysaccharide: Haemophilus influenzae type B and pneumococcal 7-valent Pure polysaccharide: Pneumococcal 23-valent, meningococcal, and Haemophilus influenzae type b Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 23 Recommended Vaccine Schedules (Textbook Box 25-6) Children/adolescents ➢ http://www.cdc.gov/vaccines/schedules/hcp/child-adolescent.html Adults ➢ http://www.cdc.gov/vaccines/schedules/hcp/adult.html Travelers ➢ http://wwwnc.cdc.gov/travel/destinations/list Pregnant women ➢ www.cdc.gov/vaccines/pubs/preg-guide.htm Health care workers ➢ www.cdc.gov/vaccines/spec-grps/hcw.htm Specific health conditions ➢ www.cdc.gov/vaccines/spec-grps/conditions.htm Other special groups ➢ www.cdc.gov/vaccines/spec-grps/default.htm Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 24 Vaccine Storage, Transport, and Handling Cold chain Routes of administration, dosage, and sites Proper timing and spacing Hypersensitivity and contraindications Documentation Vaccine safety and reporting of adverse events and vaccine-related injuries (VAERS) Vaccine needs for special groups Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 25 Prevention of Communicable Diseases Primary prevention ➢ Secondary prevention ➢ To prevent transmission of an infectious agent and to prevent pathology in the person exposed to an infection Activities to detect early and effectively treat persons who are infected Tertiary prevention ➢ Caring for persons with an infectious disease to ensure that they are cured or that their quality of life is maintained Copyright © 2015, 2011, 2007, 2001, 1997, 1993 by Saunders, an imprint of Elsevier Inc. 26
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